In finger jointing of high value lumber elements particularly those used primarily for decorative purposes, for example cedar blocks, it is important that the resultant product be homogeneous both in wood color and slope of the grain to provide a uniform, pleasing, visual appearance.
The concept of recognizing the color in different areas of a piece of lumber is not new. Such a process has been used for example in discriminating defects (e.g. knots, dark spots, etc.) and determining the location of these defects in a piece of lumber and the lumber then sawn on the basis of the location of such defects to remove or minimize the effect of the defects in the value of the lumber pieces.
It has also been proposed in Canadian patent No., 719,067 issued Oct. 5, 1965 to Finlay to use the intensity of reflected light to detect defects (by color) and to cut these defects from the wood. This patent refers to color sorting but no means for actual sorting are disclosed and no mechanism for discerning more than a color representing a defect in the background of the wood or lumber product is described.
The concept of detecting grain and particularly cross grain and in some cases torn grain using ultrasonics or microwaves coupled with light shadow techniques has also been suggested (see Szymani and MacDonald article entitled `Defect Detection in Lumber`State of the Art Forest Products Journal, Volume 31, No. 11, November, 1981).